1. Field of the Invention
The present invention relates to new and useful improvements in fans equipped with a shutter and designed for moving air into or out of a building and, more particularly, this invention relates to a fan associated with an automatic centrifugal mechanism, adapted for closing the shutter for keeping out wind, rain or other matter, when the fan is off.
2. Description of the Prior Art
Usually fans are provided with gravity shutters which, at low revolution of the fan, cannot operate efficiently because the air pressure head developed by the fan is not sufficient to keep them fully open. Moreover, during fan operation and particularly during storm weather the out-flowing air cause vibrations, noises and wear and significant pressure losses of the fan. In the past, attempts have been made to solve the various problems of said fans and said gravity shutters, whereby various centrifugal systems had been proposed. A description of the prior art known to the applicant, which is pertinent to the present application, may be found in the following Patents:
U.S. Pat. No. 4,217,816; U.S. Pat. No. 5,195,928; U.S. Pat. No. 5,288,202. In the arrangement described in U.S. Pat. No. 4,217,816, the fan comprises a shutter mechanism with two centrifugal masses that, upon rotation of the propeller, transmits an axial force to an axially reciprocating actuator. Said actuator comprises a steel rod guide sliding on a bushing.
The above system works with satisfaction for opening the shutter. However, for closing it, since at low revolutions the centrifugal forces become insignificant, but the gravity forces of the two centrifugal masses are substantially important, at each revolution of the propeller, as the two masses are vertically aligned, there is a significant friction force on said bushing and said steel rod guide may jam; therefore, the shutter will not close completely. The system described in U.S. Pat. No. 5,288,202 is similar to the previous described, therefore, the solution is not satisfactory, the friction forces are still present and the jamming of said centrifugal system is possible.
The centrifugal device described in U.S. Pat. No. 5,195,928 is well known to the applicant. Applicant developed in the past a similar mechanism using three equally spaced rotating masses and found that it works smoothly and with satisfaction, because the steel rod guide causing the aforesaid problems had been eliminated. However, this device is more expensive, comprises too many parts and joints. In addition, it requires a precise balancing and frequent maintenance.
While all the aforementioned mechanisms have the advantage to keep positively open the shutter. However, they have the disadvantage to have an axial reciprocating actuator rotatably connected to the shutter central vane. Thus, when the fan is operating, the vibrations of the propeller and of the centrifugal mechanisms are continuously transmitted to the shutter, causing undesirable noises and wear.